Various methods and systems exist for measuring stress, strain, curvature, and/or displacement of materials or structural members (e.g., objects). A strain gauge or strain gage is a device used to measure the strain of an object. The most common type of strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The gauge is attached to the object by a suitable adhesive. As the object is deformed, the foil is deformed, causing its electrical resistance to change. This resistance change, usually measured using a Wheatstone bridge, is related to the strain by the quantity known as the gauge factor.
Unfortunately, traditional strain gauges that rely on electrical resistance are limited in their applicability. First of all, such strain gauges are not ideal for measuring strain of large objects (e.g., deflections across a large distance). Second of all, resistance-based strain gauges tend to degrade when used outdoors.
Given the shortcomings of traditional strain gauges, there has been significant development in the field of optical strain gauges. Specifically, optical strain gauges have been developed to address the issues associated with measuring strain of large structures in addition to the degradation issue.